DNA encoding immunogenic gpIII glycoprotein of varicella-zoster virus

Abstract

A gene of varicella-zoster virus (VZV) which encodes immunogenic outer surface viral proteins has been identified by DNA sequence analysis. Antibodies directed against peptides imputed from the DNA sequence can react with the glycoprotein, which itself is reactive with neutralizing antibodies. The amino-terminal sequence of the purified glycoprotein is identical to a portion of the amino acid sequence imputed from the DNA sequence. This glycoprotein is useful for the preparation of a vaccine against VZV.

Description

BACKGROUND OF THE INVENTION

Chickenpox is caused by varicella-zoster virus (VZV), a member of the herpesvirus group. The disease occurs in persons with no prior VZV immunity. VZV-specific antibodies can be demonstrated shortly after onset of disease, decline during convalescence, but remain detectable for many years and correlate with immunity to the disease. Chickenpox is highly contagious; over 90% of the population becomes exposed to VZV before they are 20 years old. In most, if not all, cases, VZV apparently becomes latent in dorsal root ganglion cells. From this latent state, VZV can reactivate and cause zoster even in the presence of specific antibodies, probably as a result of weakened cellular immunity. The disease is highly morbid to the immunosuppressed and to those beyond the second decade.

VZV has five major glycoproteins on its surface: gp115 [115 kilodalton (kD) glycoprotein], gp105, gp92, gp83, gp55. These glycoproteins apparently are the products of three genes: gpIII (gp105), gpII (gp115, in the nonreduced state, composed of the reduced species gp62 and gp57), and gpI (gp92, gp83, gp55). Formerly, these genes were referred to as gA, gB, and gC, respectively. Monoclonal (McAb) and polyclonal monospecific antibodies to gA and gB display complement-independent neutralization, and such antibodies to gC display complement-dependent neutralization of VZV.

SUMMARY OF THE INVENTION

A gene of VZV which encodes the immunogenic outer surface viral glycoprotein gpIII has been identified by DNA sequence analysis. Antibodies directed against peptides imputed from the DNA sequence can react with the gpIII glycoprotein which itself is the target of neutralizing antibodies. The amino-terminal sequence of purified gpIII is identical to a portion of the amino acid sequence imputed from the DNA sequence. This glycoprotein is useful for the preparation of a vaccine for VZV.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide antigens which will prevent diseases associated with VZV infections. Another object is to provide antigens which can be used diagnostically to detect antibodies to VZV. Another object is to provide methods for the preparation of these antigens. Another object is to provide methods for using the antigens to raise antibodies to VZV. Another object is to describe the full sequence of protein antigens, which will include peptide antigens, which may be synthesized by other means or expressed in expression vectors. These and other objects of the present invention will be apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the identification of that VZV DNA segment which encodes the protective immunogenic gpIII glycoprotein. More specifically, it is directed to a 2.5 kilobase pair (kbp) DNA fragment whose respective nucleotide sequence (and derived amino acid sequence) has been located within the known sequence of the entire VZV genome. The present invention also is directed to vectors containing all or part of this 2.5 kbp DNA fragment. The invention also is directed to host cells which contain these vectors and which cells are capable of expressing all or part of the polypeptide encoded by the 2.5 kbp fragment. In accordance with known techniques, it will be obvious to those skilled in the art that parts of the foregoing polypeptide can be synthesized chemically or modified and still retain immunogenicity. Therefore, the present invention also is directed toward chemical synthesis of domains of this protein, especially domains including and surrounding hydrophilic regions and threonine or serine and asparagine-X-serine or asparagine-X-threonine residues, wherein X is any amino acid residue, since these domains are likely to reside on the outer surface of the virus.

The DNA segment which encodes gpIII is identified precisely as follows By use of immune-affinity chromatography mediated by McAb to VZV gpIII, the gpIII polypeptide is purified to 90% homogeneity. This preparation, when inoculated into guinea pigs in complete Freund's adjuvant, is capable of eliciting the production of neutralizing antibodies. This purified preparation is electrophoresed by preparative sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) and isolated on polybrene-coated glass-fiber sheets as a single 105 kD polypeptide. This sample is subjected to amino-terminal sequence analysis. Based upon a run of 7 consecutive amino acids resolved in the analysis, a pool of oligonulceotides representing every possible coding combination for the heptapeptide is synthesized. The oligonucleotide pool is radiolabelled for use as a hybridization probe to VZV DNA fragments. Specific hybridization is found to a domain within the HindIII B fragment. DNA sequence analysis of this region of HindIII B reveals a 2.5 kbp open reading frame (ORF). Within the amino acid sequence imputed from this DNA sequence, residues 18-27 form a perfect match with the amino-terminal sequence described above. Based on the imputed amino acid sequence, 3 peptides of lengths 13-22 residues are selected as likely to be immunogenic. These peptides are synthesized, coupled to bovine serum albumin, and injected into rabbits. Some of the anti-peptide sera are reactive with gpIII by Western blot analysis and by immunoprecipitation analysis. Further specificity of the anti-peptide serum is shown by the ability of anti-peptide antibodies to compete with McAb to gpIII in immunoprecipitation analysis. In addition, the anti-peptide antibodies can immunoprecipitate an 80 kD in vitro translational product of mRNA hybrid selected by the 2.5 kbp ORF.

In accordance with known techniques, it will be obvious to those skilled in the art that all or part of the above-mentioned DNA fragment can be placed into an expression vector system in order to produce all or part of the protective immunogenic polypeptide. Such an expression vector system often consists of a plasmid which is inserted into a prokaryotic or eukaryotic cell in order to direct expression of a foreign polypeptide. Such a plasmid usually contains sequences for selection of host cells containing the plasmid, amplification of plasmid copy number within the host cell, initiation of transcription of the gene for the foreign polypeptide, termination of transcription of the gene for the foreign polypeptide, in addition to the coding sequence per se which specifies the foreign polypeptide. Therefore, the present invention also is directed to host cells and vectors containing all or part of the 2.5 kbp DNA fragment. Examples of suitable host cells for expression of VZV proteins include prokaryotic cells, such as E. coli and B. subtillis, and eukaryotic cells, such as S. cerevisiae and continuous mammalian cell lines including but not limited to Chinese Hamster Ovary cells and Vero cells.

These proteins are useful individually or in combination when placed in a physiologically acceptable carrier, e.g., saline or phosphate buffered saline, to elicit neutralizing antibodies against VZV disease when administered to a member of a mammalian species, e.g., quinea pigs, in an amount of approximately 5 to 150 mcg per dose, preferably from approximately 10 to 50 mcg per dose. One or more doses may be administered to produce effective protection against VZV disease. The protein may be administered by injection, e.g., subcutaneously or intramuscularly. It is also to be understood that these proteins can be expressed directly in humans by means of appropriate viral expression vectors such as adeno, vaccinia, or herpes simplex.

The following examples illustrate the present invention without, however, limiting the same thereto. The disclosure of each reference mentioned in the following examples is hereby incorporated by reference.

EXAMPLE I

Purification of VZV gpIII Glycoprotein

Ascites fluids, carrying McAb Al (described in Keller et al., J. Virology 52: 293, 1984), were harvested from mice. An equal volume of 0.15M NaCl was added. Then, a saturated (NH.sub.4).sub.2 SO.sub.4 solution was added in an equal total volume and held at 4.degree. C. overnight. This mixture was centrifuged at 10.degree. C. and 2000 rpm. The pellet was resuspended in distilled H.sub.2 O (2 mg/ml) and dialyzed overnight against coupling buffer (0.1M NaHCO.sub.3, 0.5M NaCl, pH 8.4). One gram of cyanogen bromide-activated Sepharose 4B (Pharmacia, Piscataway, N.J.) was swollen in 0.001N HCl, then decanted into a 60 ml coarse sintered glass funnel. This was washed with 200 ml 0.001N HCl, then 50 ml coupling buffer. The Sepharose then was mixed with 10 ml of McAb solution and rotated for 2 hours at 23.degree. C. Then, 80 .mu.l ethanolamine was added and the solution was rotated for 1 hour at 23.degree. C. The resin was poured into a disposable chromatography column (BioRad), drained and washed successively with 10 ml volumes of the following solutions: 1) coupling buffer; 2) 0.1M Na.sub.2 HPO.sub.4 ; 0.5M NaCl, pH 8.2; 3) 0.1M NaOAc, 0.5M NaCl, pH 4.0; 4) 0.1M NaHBO.sub.4, pH 8.2; 5) 3M KSCN; 6) 0.1M NaHBO.sub.4, pH 8.2. Then it is stored in 0.1M NaHBO.sub.4, pH 8.2 at 4.degree. C. prior to use.

VZV glycoproteins were purified form MRC-5 human diploid fibroblasts which were infected with VZV to the extent of 80% cytopathic effect. Cells in 750 cm.sup.2 roller bottles were washed twice with 0.15M NaCl, 0.01M Na.sub.2 HPO.sub.4, pH 7.2 and drained well. Ten ml of 50 mM Tris, pH 7.5, 2% Triton X-100, 4 mM phenylmethylsulfonylfluoride (PMSF) were incubated 15 minutes to the bottle while rolling. The same 10 ml then were used successively to extract 9 more roller bottles. A fresh 10 ml aliquot of buffer was used successively to rinse the 10 roller bottles and pooled with the first aliquot, such that 20 ml of extract represent material from 10 roller bottles. Extracts were stored at -70.degree. C. until use. Extracts were thawed and dialyzed overnight at 4.degree. C. against 0.15M NaCl, 0.01M Na.sub.2 HPO.sub.4, 0.05% Triton X-100, pH 7.2, then clarified by centrifuging at 1500 rpm for 15 minutes at 4.degree. C. Extract (20 ml) was added to 1 g of McAb-coupled resin and incubated overnight at 4.degree. C. with shaking. The slurry was centrifuged for 15 minutes at 1500 rpm at 4.degree. C. and washed three times with 0.1M NaHBO.sub.4, pH 8.2. The glycoprotein was eluted by incubation at 23.degree. C. with 10 ml 3M KSCN. The eluate immediately was dialyzed against 0.15M NaCl, 0.01M Na.sub.2 HPO.sub.4, 0.05% Triton X-100, pH 7.2 overnight at 4.degree. C. and concentrated to approximately 1 mg/ml.

This peak was verified as VZV gpIII by the following criteria. In silver stains of SDS-PAGE run under reducing conditions, the sample was resolved as one polypeptide species of molecular weight 105 kD as described in Keller et al., ibid., i.e., gp105; Shiraki et al., J. Gen. Virology 61: 255 (1982), i.e., gPl; Grose et al., Inf. Immun. 40: 381 (1983), i.e., gp118, Forghani et al., J. Virology 52: 55 (1984), i.e., 118K. In addition, a parallel aliquot of [.sup.35 S]-methioninelabelled cell extract purified by the technique could be immunoprecipitated specifically with McAb to gpIII, resulting in the resolution by SDS-PAGE of a single 105 kD species.

EXAMPLE II

Purified VZV gpIII polypeptide induces antibodies which neutralize VZV infectivity in vitro

Guinea pigs were inoculated intramuscularly with 20 micrograms in complete Freund's adjuvant of VZV gpIII (purified by immune-affinity chromatography as described above in Example I), followed one month later by two inoculations each of ten micrograms of VZV gpIII in incomplete Freund's adjuvant spaced two weeks apart. Sera were obtained from the guinea pigs after these three inoculations. Each of the guinea pig sera was utilized in an in vitro VZV neutralization assay as described (Keller et al., ibid.). By this assay, the post-immunization, but not the pre-immunization sera, contained VZV-neutralizing antibodies.

EXAMPLE III

N-Terminal amino acid sequence of purified VZV qpIII polypeptide

200 .mu.g of VZV gpIII, prepared as described in Example I, were electrophoresed by preparative SDS-PAGE (7.5% polyacrylamide) and isolated on polybrene-coated glass-fiber sheets as a single polypeptide of 105 kD [van de Kerckhove et al., Eur. J. Biochem. 152: 9 (1985)]. This sample was subjected to amino-terminal sequence analysis using an Applied Biosystems Gas-Phase Sequenator [Hewick et al., J. Biol. Chem. 256: 7790 (1981)]. The phenylthiohydantoin amino acids produced at each step were separated and quantitated by high performance liquid chromatography [Speiss et al., Proc. Nat. Acad. Sci. U.S.A. 70: 2974 (1979)]. The sequence analysis demonstrated that gpIII contains a single unblocked amino-terminus. As shown in Table I, this sequence (with 2 gaps) can be aligned perfectly with amino acids 18-27 in Example V (see below) which have been imputed from the DNA sequence of the 2.5 kbp ORF.

TABLE 1______________________________________N-Terminal amino acid sequence of purified VZV gpIII______________________________________1 asn lys ser tyr val thr pro thr pro ala2 18 19 20 21 22 23 24 25 26 273 -- lys ser tyr val thr pro thr -- ala______________________________________ 1 = imputed amino acids from Example V. 2 = amino acid position in the ORF of sequence 1. 3 = amino acid sequence of purified VZV gpIII, wherein a dash (--) means that no amino acid was resolved at that position in the analysis.

EXAMPLE IV

Use of oligonucleotides based on amino acid sequence data to identify the gpIII gene

Based on the N-terminal amino acid sequence of gpIII, derived as described in Example III and presented in Table 1, a pool of oligonucleotides was designed which represents every possible combination of DNA sequences capable of encoding this amino acid sequence. This pool is ##STR1##

These oligonucleotide pools were labelled with [.sup.32 P] ATP in the presence of T4 polynucleotide kinase. The probe was hybridized to a Southern blot of HindIII fragments of VZV. By this analysis, the above gene sequence was localized to the HindIII B fragment.

EXAMPLE V

Determination of nucleotide sequences of the 2.5 kbp segment of VZV DNA

The complete nucleotide sequence of the VZV HindIII-B DNA segment contains several large ORFs. One of these ORFs is 2.5 kbp in length, encodes a 90 kD protein, and contains a DNA sequence (Example IV) which codes for the amino terminal gpIII sequence in Example III. The nucleotide sequence for the complete 2.5 kbp segment which encodes the gpIII glycoprotein is given below: ##STR2##

The foregoing nucleotide sequences encode the following peptide: ##STR3##

EXAMPLE VI

Based on the DNA sequence of Example V and its imputed amino acid sequence, 3 domains were chosen for the synthesis of peptides which would be likely to elicit the production of antibodies against gpIII. These domains are: 1) phe.sup.152 -pro.sup.173 (22-mer), 2) glu.sup.793 -tyr.sup.804 (12-mer), and 3) gly.sup.828 -thr.sup.841 (14 mer). The first 2 were obtained from Peninsula Laboratories Inc. The latter was synthesized on an Applied Biosystems Inc. 430A solid-phase peptide synthesizer. All synthetic peptides, with an amino-terminal acetyl group and a carboxy-terminal hydroxyl group, were characterized by reversed-phase high performance liquid chromatography and amino acid analysis. Each peptide was conjugated to bovine serum albumin according to established techniques [Walter et al., Proc. Natl. Acad. Sci. USA 77:5197 (1980); Gutkowska et al., Biochem Biophys. Res. Commun. 122:593 (1984)]. A quantity, 5-10 mg/1.0 ml, of each conjugate was injected into rabbits intramuscularly in complete Freund's adjuvant at week 0 and in incomplete Freund' s adjuvant at week 4. Rabbits were bled at week 8. Sera were utilized in Western blot analysis at 1:500 dilutions. The antisera recognized a 105 kD polypeptide. In immunoprecipitation analyses, 1:30 dilutions of sera that were incubated with [.sup.35 S] methionine-labelled infected cell extracts immunoprecipitated a 105 kD polypeptide. The 105 kD species was conclusively demonstrated to be gpIII by virtue of the ability of McAb to gpIII (Al in Keller et al., ibid.), but not McAb to gpI or gpII (C5 and B1, respectively in Keller et al., ibid.), to preclear the 105 kD polypeptide from the lysate by 2 successive immunoprecipitations, as shown by abrogation of the immunoprecipitability of the 105 kD polypeptide by the anti-peptide sera.

EXAMPLE VII

The 2.5 kbp DNA ORF can select RNA encoding the precursor protein to gpIII

Cystoplasmic RNA was prepared from VZV-infected MRC-5 cells as described (Chirgwin et al., Biochemistry 18 5294 (1979). The RNA encoded by the 2.5 kbp ORF in the VZV HindTTT B fragment as well as nonselected RNA and RNA selected by other fragments were selected by hybridization to cloned VZV DNA fragments [Ecker & Hyman, Proc. Natl Acad. Sci. USA 79:156 (1982)] bound to nitrocellulose [Cooper et al., J. Virology 37: 284 (1981)]. These RNAs were translated in a rabbit reticulocyte lysate. The polypeptide products were immunoprecipitated by one polyclonal monospecific rabbit antibody raised to the synthetic peptide described in Example VI. By this analysis, it was found that an 80 kD in vitro translational product from mRNA selected by the 2.5 kbp ORF in the VZV HindIII-B fragment could be immunoprecipitated by the anti-peptide sera.

Claims

1. A 2.5 kbp fragment of VZV DNA having the nucleotide sequence: ##STR4## or a subportion of the foregoing sequence encoding an immunogenic epitope selected from the group consisting of phe.sup.152 -pro.sup.173 ; glu.sup.793 -tyr.sup.804 ; and gly.sup.828 -thr.sup.841.

2. An expression vector containing all or part of the 2.5 kbp DNA fragment having the nucleotide sequence. ##STR5## or a subportion of the foregoing sequence encoding an immunogenic epitope selected from the group consisting of phe.sup.152 -pro.sup.173 ; glu.sup.793 -tyr.sup.804 ; and gly.sup.828 -thr.sup.841.

3. A suitable prokaryotic or eukaryotic host cultured cell containing a vector according to claim 2.

4. An expression vector according to claim 2 wherein said sequence is expressed directly in a mammalian species.